Laser materials processing as known in the art and used herein refers to performance of materials processes, such as cutting, welding, drilling and soldering, using a continuous wave or pulsed laser beam. The average power of such a laser beam may range from as little as approximately one watt to hundreds of watts, the specific power being selected on the basis of the particular process being performed. Laser beam power required for materials processing generally is much greater than laser beam power required for other laser-based systems such as communication systems.
A laser beam source, i.e., a laser resonator, typically includes a laser head having a crystal, such as a face-pumped laser as described in commonly assigned U.S. Pat. No. 3,633,126, "Multiple Internal Reflection Face-Pumped Laser", disposed therein. The crystal may, for example, have a rectangular cross-sectional shape and have six surfaces including respective pumping and cooling surfaces. In operation, energy is injected, i.e. pumped, into the crystal through the pumping surfaces. Laser crystal flashlamps, sometimes referred to herein as laser flashlamps, disposed within the laser head and along axes parallel to the pumping surfaces usually are utilized as pumping means. The laser flashlamps are coupled to a high energy power supply. The crystal is cooled, for example, by flowing coolant along the crystal surfaces. As is known in the art, the slab crystal has two crystal surfaces which are finished to brewster's angle. When operating as a laser resonator, a beam to be utilized for processing is emitted from one of the finished crystal surfaces.
Optical components such as lenses and mirrors form part of the laser resonator and are disposed for extracting a high power laser beam from the crystal volume. A beam expanding lens combination and a focusing lens may be aligned with the laser resonator for shaping an emitted beam to be utilized in processing.
A laser head may operate in a pulsed mode or in a continuous mode. A pulsed mode means that pulses of beams are emitted from the laser resonator. Such pulses of beams are obtained by exciting, i.e., energizing, the crystal with pulses of energy, e.g., pulsing the laser flashlamps. A continuous mode means that a continuous beam is emitted from the laser resonator. Such a continuous beam is obtained by providing continuous energy to the crystal, e.g., by leaving the laser flashlamps on.
A laser head may be configured to operate as a laser oscillator or as a laser amplifier. When operating as an oscillator, the crystal is excited to a state wherein the crystal emits electromagnetic energy. When operating as an amplifier, the crystal is excited and, simultaneous with crystal excitation, a beam of electromagnetic energy from a separate source is injected into the crystal. As the beam travels through the crystal, it is amplified due to the excited state of the crystal. An amplified beam is then emitted from the finished surface of the crystal.
In operation of the crystal in either mode, energy emitted from the laser flashlamps is injected into the crystal, through the pump surfaces, and excites, or optically pumps, the crystal. The laser beams generated are very narrow beams of radiation and the intensity within the beams is exceptionally high.
Fast pulse repetition rates or long continuous mode operation of the crystal causes heat to be generated within the crystal. The crystal, in normal operation, may be cooled by flowing a coolant along the crystal cooling surfaces. If an optical component, e.g., a mirror, within the laser resonator becomes damaged or if some other abnormality occurs within the laser source during an operation, the crystal could discontinue lasing, i.e., discontinue emitting a laser beam. The laser flashlamps, however, will continue pumping the crystal. More specifically, if the laser flashlamps are pumping the crystal above the lasing threshold, and if the crystal is not emitting a laser beam, then parasitics i.e., irregular lasing paths, may develop within the crystal. The appropriate action in these circumstances usually is to stop energizing the crystal, such as by turning off the laser flashlamp power supply.
Damaging optical components, and especially the crystal, is undesirable because, among other things, laser crystals are expensive and replacements may not be readily available. Also, if a component becomes damaged, the laser source usually must be shut down to make repairs. Shutting down operation of the laser source for a long period of time may be very costly, especially if the laser source is part of an assembly line. The whole line may have to be shut down as a result of laser source failure.
It would be beneficial, therefore, to provide a means for detecting abnormal operations within a laser source so that timely appropriate actions may be taken to prevent damage, or further damage, to the crystal and other optical components.
It would also be beneficial to provide means for detecting abnormal operations throughout an entire laser processing system. For example, a laser system may include, in addition to a laser source, an optical fiber and an output coupler. Transmission of laser beams through optical fibers, at power levels suitable for performing materials processing, greatly enhanced the flexibility of laser-based materials processing systems. Various techniques for the efficient injection of a high power laser beam from a laser source into an optical fiber for transmission therethrough are disclosed, for example, in commonly assigned U.S. Pat. Nos. 4,564,736; 4,676,586; and 4,681,396 respectively entitled "Industrial Hand Held Laser Tool and Laser System", "Apparatus and Method for Performing Laser Material Processing Through a Fiber Optic", and "High Power Laser Energy Delivery System". Generally, lenses adjacent a laser source are utilized to focus a beam onto an input end of an optical fiber, and these lenses may be referred to herein, collectively, as a fiber injection unit.
An output end of the optical fiber is disposed in an output coupling device, sometimes referred to herein as an output coupler, which includes means to collimate and focus the beam emitted from the fiber output end. The output coupling device is moved relative to a workpiece by, for example, a computer-controlled robotic arm. With optical fiber transmission, a system user must monitor, during the processing and in addition to the laser source, a fiber injection unit, an output coupler, and an optical fiber. Failure of any one component may result in failure of the entire system.
Also available to enhance laser materials processing are systems for time sharing of a materials processing laser beam among a plurality of optical fibers. Such systems are described in commonly assigned U.S. Pat. Nos. 4,739,162 and 4,838,631 entitled "Laser Beam Injecting System" and "Laser Beam Directing System", respectively. Manufacturers of beam time sharing systems include Robolase Systems, Inc. of Costa Mesa, Calif. and Lumonics Corporation of Livonia, Mich. By the use of such beam time sharing systems, a beam generated by one laser source can be shared among multiple optical fibers. The respective output ends of each optical fiber may be positioned proximate respective process points on one or more workpieces. Laser beam time sharing systems, sometimes referred to herein as multiplexers, have further increased the flexibility and efficiency of laser materials processing. With a multiplexer-based laser system, the system user must monitor a laser source, a multiplexer, multiple beam injecting systems, multiple couplers, and multiple optical fibers. The sequence of optical components in such systems is sometimes referred to herein as an optical train.
A monitoring system for monitoring laser system components preferably facilitates obtaining desired processing results and aids in preventing damage to the components. The monitoring system, however, should not slow down laser materials processing operations. Otherwise, advantages of utilizing optical fiber/laser technology, such as a reduction in processing time, may be lost. Further, it is preferred that the monitoring system operate in substantially real-time. The monitoring system preferably should be able to obtain data simultaneous with materials processing so that if adjustments to components are needed, such adjustments can be made before further damaging processing components.
It is therefore an object of the present invention to provide a system for monitoring and detecting an onset of abnormal operation of laser processing components so that appropriate action, such as laser flashlamp power supply turn-off, may be taken in a timely manner.
Another object of the present invention is to provide a system for monitoring laser source operation including the performance of optical components disposed within the laser source.
Still another object of the present invention is to provide a system for monitoring laser beam transmission through an optical fiber and through output coupler optical components.
Still yet another object of the present invention is to provide a system which monitors, in substantially real time, laser materials processing components in a manner that does not slow laser materials processing.